The present invention relates to a method for fabricating an electrode wiring structure with fine contacts with a high aspect ratio formed on a shallow junction which have low contact resistance and reduced leakage, and a semiconductor integrated circuit device using such wiring structure.
As is well known, when contacts for electrodes of a semiconductor device are miniaturized and the aspect ratio is increased, the following problems occur. The first problem is that the aluminum wiring containing silicon, which is used as an electrode contact with mono-crystalline silicon, increases the contact resistance due to the silicon precipitation in a sintering step. The second problem is that the conventional electrode structure made by sputtering does not permit metal to invade into contacts due to the high aspect ratio and so may disconnect from the semiconductor device. In order to solve the above problems, a technique of selectively filling tungsten (W) through CVD (chemical vapor deposition) as shown in FIG. 4 has been developed, as disclosed in IEDM 87 9-5 "A Highly Relaible CVD-W Utilizing SiH.sub.4 Reduction for VLSI contacts".
In FIG. 4, 9 is a silicon (Si) substrate; 10 is an n.sup.+ highly doped diffused layer; 11 is an inter-layer insulator layer; 13 is tungsten (W) selectively filled in the contact 12 through CVD; 15 is an aluminum electrode; 14 is a boundary between the tungsten area and the aluminum electrode; and 50 is a boundary between the tungsten area and, the insulator film 11. In such an electrode structure, tungsten 13 is filled in the contact 12 so that the aspect ratio of the contact exceeding 1 is improved and so the electrode will not disconnect from the diffused layer 10.
The sintering step, however, diffuses aluminum 15 through the boundary 50 between the tungsten area 13 and the insulator layer 11 so that aluminum 15 may invade into the diffused layer as indicated by 16 through the reaction of the diffused layer with aluminum and tungsten thereby to destroy the junction in the diffused layer 10; incidentally aluminum does not diffuse through the boundary 14 because tungsten 13 serves as a sufficient barrier against aluminum.
In order to prevent aluminum from invading into a silicon (Si) substrate in the sintering step, barrier metal deposited by sputtering as shown in FIG. 5 is usually used. This technique, however, provides poor step coverage for the contact having an aspect ratio exceeding 1 and so cannot sufficiently prevent the invasion of aluminum.
In FIG. 5 17 is an Si substrate; 18 is a highly doped diffused layer; 19 is an inter-layer insulator film; 20 is a contact having an aspect ratio exceeding 1; 21 is a barrier metal of TiN (titanium nitride); and 22 is an aluminum electrode. As seen from FIG. 5, the barrier metal is broken as indicated by 21-1 so that the electrode 22 is disconnected from the diffused layer 18.
The above problems become remarkable as the junction layer below the contact is shallow and the aspect ratio of the contact is large.